We intend in the future to continue our studies on the regulatory mechanisms of skeletal and smooth muscles. With the skeletal system we hope to use fluorescent dyes to estimate whether selected components of the regulatory complex move relative to each other as a result of changes in the Ca2 ion concentration. This information will add considerably to our knowledge of the various interactions between the thin filament proteins that are important to the regulatory mechanism. In smooth muscle the regulatory mechanism is different, and is centered on the Ca2 ion dependent phosphorylation of the myosin molecule. We will try to isolate and characterize the various components that are involved. It is anticipated that in order for the phosphorylation to be effective as a regulatory mechanism at least two enzymes are required, a kinase and a phosphatase. We will attempt therefore to define more precisely the role that each plays in the control mechanism.